The present invention relates to novel flame-retardant polypropylene resin compositions, which have been improved in incombustibility and other physical properties. More specifically, the present invention relates to incombustible polypropylene resin compositions prepared by dispersing polyphenylene ether-based resin, phosphorus flame-retardant and flame-retardant auxiliary agent in the major component, polypropylene resin in a specific ratio.
Since they have excellent processability, chemical resistance, weather resistance and mechanical strength, polypropylene resins have been widely used in various fields including household electrical appliances, building materials, interior decorative materials, automobile parts, etc. However, they need to be supplemented with a variety of organic or inorganic flame-retardants in order to obtain incombustibility required for these uses.
Exemplary incombustible polypropylene resin compositions containing such flame-retardants include compositions comprising polypropylene resin and hydrated inorganic compound such as magnesium hydroxide, aluminum hydroxide and hydrotalcite (See: Japanese Laid-open Publication Nos. 53-92855, 54-29350, 54-77658, 56-25954, 57-87462 and 60-110738); compositions comprising polypropylene resin, polyethylene resin with a melt index of 0.01xcx9c2.0, halogen compound (for example, decabromodiphenyl ether or dodecachloro-dodecahydromethanodibenzocyclooctene), and inorganic filler selected from the group consisting of stone powder, kaolin, celestite, silica and diatomite (See: Japanese Laid-open Publication No. 55-30739); and compositions comprising polypropylene resin and either a reaction product, which is generated from a reaction between an aldehyde compound and a nitrogenous compound wherein xe2x95x90Cxe2x95x90O (or xe2x95x90Cxe2x95x90S or xe2x95x90NH) group is incorporated into ammonium phosphate (or amine phosphate) ring structure, or an oligomer (or polymer) of 1,3,5-triazine derivatives (See: Japanese Laid-open Publication Nos. 52-146452 and 59-147050).
However, the compositions, which were prepared by adding inorganic compound such as magnesium hydroxide to polypropylene resin so as to obtain highly incombustible resin composition, have been found to be poor in their plasticity. On the other hand, the compositions prepared by adding decabromo phenyl-based compound to polypropylene resin are relatively good in their plasticity and incombustibility, but are disadvantageous in that they generate poisonous gases during secondary processing or combustion.
In contrast, the compositions disclosed in Japanese Laid-open Publication Nos. 52-146452 and 59-147050 do not show the decline of secondary processing property as well as the production of corrosive and poisonous gases. Also, these compositions exhibit the incombustibility of V-0 at {fraction (1/16)} inch thickness when tested according to the vertical firing test protocol out of xe2x80x9cCOMBUSTIBILITY TESTS OF PLASTIC MATERIALS FOR MACHINE PARTSxe2x80x9d of UL Subject 94(Underwriters Laboratories Incorporation). Nonetheless, these compositions are inferior in thermal resistance and impact strength, so they are unsuitable to be used in machine parts requiring these physical properties.
On the other hand, polyphenylene ether resins have been known as highly efficient plastics having excellent incombustibility, thermal resistance, size stability, non-hydroscopicity and electric properties. Therefore, an improved resin composition, which would advance in plasticity, impact resistance, thermal resistance and incombustibility and thus could be used in extensive areas, may be expected when mixing a polypropylene resin with a polyphenylene ether resin and thereby making up for each other""s demerits and making use of each other""s merits. For this reason, various polyolefin/polyphenylene ether-based polymer alloys have been vigorously proposed in the art. For example, U.S. Pat. No. 3,994,856 describes blending of polyphenylene ether with polystyrene-based hydrogenated block copolymer for the purpose of improving impact resistance and solvent resistance. U.S. Pat. No. 4,145,377 discloses thermoplastic resin compositions, which were enhanced in impact resistance and solvent resistance by blending either polyphenylene resin or a mixture of polyphenylene resin and styrene-based resin together with both a pre-mixture consisting of 20xcx9c80 weight parts of polyolefin and 80xcx9c20 weight parts of hydrogenated block copolymer and hydrogenated block copolymer. U.S. Pat. Nos. 4,166,055 and 4,239,673 teach improvement of impact resistance by blending polyphenylene ether with both hydrogenated block copolymer and polyolefin. Similarly, U.S. Pat. No. 4,383,082 and European Patent No. 115712 also teach improvement of impact resistance by blending polyphenylene ether with both polyolefin and hydrogenated block copolymer. Further, Japanese Laid-open Publication Nos. SHO 63-113058, SHO 63-225642, HEI 3-72512, HEI 4-183748 and HEI 5-320471, and U.S. Pat. No. 4,863,997 disclose resin compositions having advanced chemical resistance and processability, which were prepared by adding a particular hydrogenated block copolymer as a modifier to a blend of polyolefin resin and polyphenylene ether resin. In addition, Japanese Laid-open Publication No. HEI 7-53859 discloses incombustible resin compositions prepared by adding halogen-containing phosphoric ester compound and antimony compound to a blend of polyolefin resin and polyphenylene ether resin.
The polymer alloy compositions obtained from the above prior arts provide improved resin compositions, which take advantages of polyolefin resin and polyphenylene ether resin concerning thermal resistance, mechanical strength and processability. However, these polymer alloy compositions are still poor in incombustibility, and therefore require a large amount of flame-retardant, which results in significant decrease in mechanical strength. Meanwhile, Japanese Laid-Open Publication No. HEI 11-140245 describes preparation of thermoplastic incombustible resin compositions by adding an aromatic phosphoric ester compound and a 1,3,5-triazine-based nitrogenous compound to a blend of polyphenylene ether resin and hydrogenated copolymer. In our test, however, these compositions did not succeed in showing incombustibility of UL94 V-0, and were found to have difficulties in ensuring practical thermal resistance because of steep decrease in thermal resistance.